CB-602: guard against a config key that never reaches the example

BridgedConfig.KNOWN_TOP_LEVEL_KEYS is now package-private so a test can assert
every key the parser accepts appears in bridged.example.yaml — live or
commented-out, since the file is gitignored and the example is the only
committed description of the config schema. The existing tests only checked
the example->code direction; this adds code->example.

bridged/src/main/java/dev/ltms/bridged/config/BridgedConfig.java

@@ -967,8 +967,12 @@ public record BridgedConfig(
     /**
      * Top-level keys this version understands. Used only to warn about the rest — see
      * {@link #warnUnknownTopLevelKeys}. Keep in step with the record components.
+     *
+     * <p>Package-private (not {@code private}) so a test can assert every key here is documented in
+     * {@code bridged.example.yaml} — the only committed description of the config schema, since
+     * {@code bridged.yaml} itself is gitignored.
      */
-    private static final Set<String> KNOWN_TOP_LEVEL_KEYS = Set.of(
+    static final Set<String> KNOWN_TOP_LEVEL_KEYS = Set.of(
             "bind", "herdrSocket", "profiles", "guard", "worktreeRoot",
             "lifecycle", "spawnReadyTimeoutMs", "spawnReadyPollMs", "broker", "primary", "fleet",
             "leadHeartbeat", "health", "placement", "auth", "configReload", "quarantineCooldownSeconds");

bridged/src/test/java/dev/ltms/bridged/config/BridgedConfigTest.java

@@ -10,6 +10,7 @@ import java.nio.file.Path;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.regex.Pattern;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -1189,6 +1190,79 @@ class BridgedConfigTest {
         assertEquals(5, cfg.leadHeartbeat().quietNudgeCap());
     }
 
+    /**
+     * A top-level key {@code BridgedConfig} reads but that appears nowhere in
+     * {@code bridged.example.yaml} — live or commented — is invisible drift: {@code bridged.yaml}
+     * is gitignored, so the example is the ONLY committed description of the config schema, and
+     * neither {@link #shippedExampleConfigParses} (example → code: does the example still parse)
+     * nor {@link #everyOptionalKnobDocumentedInTheExampleBinds} (a hand-maintained list of keys
+     * that must bind) can catch a brand-new key nobody added to either.
+     *
+     * <p>This test compares the OTHER direction: every key in {@link BridgedConfig#KNOWN_TOP_LEVEL_KEYS}
+     * (the parser's own accepted set, which backs the unknown-key WARN) must appear as a top-level
+     * key in the example text, live or commented-out — see {@link #topLevelKeyDocumented}.
+     */
+    @Test
+    void everyKnownTopLevelKeyIsDocumentedInTheExample() throws Exception {
+        Path example = Path.of("bridged.example.yaml");
+        assertTrue(Files.exists(example), "bridged.example.yaml must ship next to the pom");
+        String text = Files.readString(example);
+
+        List<String> undocumented = BridgedConfig.KNOWN_TOP_LEVEL_KEYS.stream()
+                .filter(key -> !topLevelKeyDocumented(text, key))
+                .sorted()
+                .toList();
+
+        assertTrue(undocumented.isEmpty(), () -> "key(s) " + undocumented
+                + " are read by BridgedConfig but appear nowhere in bridged.example.yaml — "
+                + "document each one there, commented out if optional. bridged.yaml is "
+                + "gitignored, so this file is the only committed description of the config "
+                + "schema an operator or a worker can see.");
+    }
+
+    /**
+     * Most of {@code bridged.example.yaml} is deliberately commented out — optional sections are
+     * documented as commented blocks so the shipped file stays a working minimal config. A key
+     * documented ONLY as a comment must still count as documented; parsing the file as YAML and
+     * reading its live key set (as an earlier attempt at this guard did) gets this wrong, because
+     * every commented section then looks entirely absent.
+     */
+    @Test
+    void commentedOnlyTopLevelKeyCountsAsDocumented() {
+        String yaml = """
+                bind:
+                  port: 8765
+                # broker:
+                #   uri: amqp://guest:guest@127.0.0.1:5672
+                """;
+        assertTrue(topLevelKeyDocumented(yaml, "broker"),
+                "a key documented only inside a commented-out block must still count as documented");
+    }
+
+    /** A key that appears in neither a live nor a commented top-level line must NOT count. */
+    @Test
+    void absentTopLevelKeyIsNotDocumented() {
+        String yaml = """
+                bind:
+                  port: 8765
+                """;
+        assertFalse(topLevelKeyDocumented(yaml, "broker"),
+                "a key mentioned nowhere in the example must not be reported as documented");
+    }
+
+    /**
+     * True when {@code key} appears as a top-level YAML key in {@code yaml} — either live
+     * ({@code key:} at column 0) or commented out ({@code # key:}, also at column 0, with only
+     * whitespace between the {@code #} and the key). Anchoring on column 0 is what keeps this a
+     * top-level check: an indented occurrence (a nested field, or prose inside a comment that
+     * happens to end in a colon) never matches, because {@code ^} requires the key's own first
+     * character — or the sole leading {@code #} — to sit at the very start of the line.
+     */
+    private static boolean topLevelKeyDocumented(String yaml, String key) {
+        Pattern p = Pattern.compile("(?m)^(?:#\\s*)?" + Pattern.quote(key) + ":");
+        return p.matcher(yaml).find();
+    }
+
     @Test
     void placementDefaultsToFixedForExistingConfigs(@TempDir Path dir) throws Exception {
         Path f = dir.resolve("no-placement.yaml");